New pressure-induced phase changes in CdWO₄ from Raman spectroscopic and optical microscopic studies

Pressure-induces phase transitions in ABO4 tungstates and molybdates with scheelite and wolframite structure are of interest to materials science and mineral physics. High-pressure phases with interesting physical properties can be expected. Through a high-pressure Raman and optical microscopic study we have found two novel pressure-induced phase transitions in wolframite-type CdWO4. The first transition near 10 GPa is subtle, but easily observable under the polarizing microscope, as the crystal breaks into domains of colour, presumably due to a phase change accompanied by twinning, or ferroelasticity. At the second transition near 20 GPa, the Raman data clearly indicate a change in W-O coordination from basically tetrahedral to truly octahedral, a new finding of significance to high-pressure crystal chemistry